F with 7 electrons has a net neutral charge, but it wants to complete its valence orbital with one more electron. The attraction of this electron makes it an electrophile. Once it has 8 electrons and a net negative charge of one, it is no longer an electrophile.

F is a halogen which have high electronegativity and want to gain a single electron to complete a full octet of valence electrons. However, in some reactions involving diatomic halogens F (and other halogens) can act as an electrophile and nucleophile (in this case it'd be two different F atoms.

F is a halogen which have high electronegativity and want to gain a single electron to complete a full octet of valence electrons. However, in some reactions involving diatomic halogens F (and other halogens) can act as an electrophile and nucleophile (in this case it'd be two different F atoms.